President Trump urged Senate Judiciary Chairman Lindsey Graham on Thursday to call former President Barack Obama as the first witness in any hearing about spying on the Trump campaign in 2016, saying Mr. Obama “knew everything.”

“If I were a Senator or Congressman, the first person I would call to testify about the biggest political crime and scandal in the history of the USA, by FAR, is former President Obama,” Mr. Trump said. “He knew EVERYTHING. Do it @LindseyGrahamSC, just do it. No more Mr. Nice Guy. No more talk!”

Intelligence documents released Wednesday by two Republican senators show that several high-level Obama administration officials were involved in “unmasking” Trump National Security Adviser Michael Flynn as part of the Russia investigation during the transition before Mr. Trump’s inauguration. They included former Vice President Joseph R. Biden, the presumptive Democratic presidential nominee.